Understanding brain-behavior relationships is one of the most challenging current scientific problems. The workings of the brain are barely understood and the functional organization of the mind remains a matter of much speculation and controversy, which makes it all the more difficult to figure out the relationships between the two entities. Most of our knowledge of such relationships comes from the study of cognitive impairments resulting from cerebral injury, and the study of patients provides the opportunity to establish correlations between symptoms and anatomical structures, and to obtain information about the break-down of mental functions that provides a window on the organization of the cognitive architecture. Yet, because of a lack of one-to-one correspondence between structure and function and of the dynamic effects of a cerebral lesion on brain functioning, the study of patients presents limitations for inferences about brain-behavior relationships. A complementary approach to the study of this issue is provided by positron emission tomography (PET) measurements of regional cerebral blood flow (rCBF) in normal subjects performing cognitive tasks, and the objective of this project is to seek additional and converging evidence bering on brain-behavior relationships in the area of visual cognition and representation of knowledge, with a special emphasis on the processing of faces and the access to knowledge about individuals. The starting point of this project is a computational model of face and person recognition which specifies some of the component operations that must be implemented to achieve a specific goal. Using a series of successive and complementary tasks that differ from one another in few component operations, PET measurements of rCBF will be carried out in normal subjects, and these tasks will also be carried out on these subjects, brain-damaged patients, and prosopagnosic patients in a laboratory context. Specific questions will be addressed in an attempt to uncover the functional organization of neural structures underlying various operations on faces, and they will be concerned with access to semantic and nominal knowledge about an individual, separate and conjoint processing of faces and names related to the same individual, processing of "categorical" objects as opposed to "unique" objects, correcting for departure of the stimulus from its canonical view or orientation, perceptual operations depending on the configurational or featural nature of the processes that have to be implemented. Physiological evidence of regional cerebral activation will be compared with the sites of lesion of neurological patients who find themselves defective at performing the corresponding tasks. Thus, in addition to providing reciprocal constraints for interpretation and understanding the neurobiological substrates of face processing, the results from these different sources will provide the opportunity to better identify the respective strengths and weaknesses of these experimental approaches and to understand the dynamics of brain functioning with lesser degrees of freedom than either one would allow on its own.